As it is well known, the power delivered by an internal-combustion engine depends on the amount of air fed into the combustion chamber of this engine. This amount of air is itself proportional to the density of this air. Therefore, if high power is required, this amount of air is increased by compressing the air prior to feeding it into the combustion chamber. This operation is more commonly referred to as supercharging and it can be performed by a supercharging device such as a turbosupercharger or a driven compressor such as a screw type compressor.
In order to increase this amount of air supplied to the cylinder, an intake mode with a residual burnt gas scavenging stage is provided. This scavenging allows, before the end of the engine exhaust phase, to discharge the burnt gases present in the combustion chamber and to replace them by supercharged air.
As explained in patent U.S. Pat. No. 4,217,866, this scavenging stage consists in performing, at the end of the engine exhaust phase and at the beginning of the intake phase, overlapping of the exhaust and intake valves of a cylinder. This overlap is obtained by opening simultaneously these exhaust and intake valves for some degrees to some ten degrees of crankshaft rotation angle.
In the indirect-injection supercharged engine example described in this document, at least one burnt gas exhaust means with an exhaust valve controlling an exhaust pipe and at least two intake means are provided. One of the intake means is an intake means for non-carbureted supercharged air with a pipe and a valve, and the other intake means is an intake means for carbureted air, consisting of a pipe provided with a fuel injection nozzle and a valve.
Burnt gas scavenging is carried out, on the one hand, through overlap of the exhaust valve and of the non-carbureted supercharged air intake valve, the carbureted air intake valve remaining closed and, on the other hand, by the fact that the pressure of the air at the open intake valve is higher than the pressure of the exhaust gases still present in the combustion chamber. The non-carbureted supercharged air that is allowed into the combustion chamber scavenges these gases so as to discharge them through the exhaust valve. The non-carbureted supercharged air thus occupies the volume freed by these exhaust gases, which allows to quite significantly increase the amount of air supplied during the engine intake phase. Near the end of the scavenging stage, the exhaust valve closes, the carbureted supercharged air intake valve opens, the fuel injection nozzle is activated and carbureted supercharged air is fed into the combustion chamber through the other intake means as a complement to the non-carbureted supercharged air supplied.
Although this type of engine runs satisfactorily, it involves drawbacks that are by no means insignificant.
In fact, during conventional running of the engine following this scavenging stage and which requires no scavenging stage, the two intake valves remain simultaneously open during the engine intake phases. This has the effect of supplying carbureted air through one pipe and non-carbureted air through the other pipe. In the combustion chamber, mixing with these two types of air is difficult and occurs in such a way that the mixture is not homogeneous. This lack of homogeneity thus creates pollutants during combustion of this mixture. Furthermore, to obtain an average fuel/air ratio close to 1 for the fuel mixture in the combustion chamber, a large amount of fuel has to be injected into the carbureted air intake pipe with a fuel/air ratio close to 2. This large amount of fuel consequently generates, upon engine cold start-up, pollutants in form of unburned hydrocarbons (HC) during combustion of the mixture in the combustion chamber.
The present invention aims to overcome the aforementioned drawbacks by means of an engine air intake control method allowing better homogenization of the fuel mixture contained in the combustion chamber, as well as fuel consumption and emissions reduction.